Barium-containing compounds which have the potential to serve as sources in organometallic chemical vapor deposition are scarce. Initially reported over fifty years ago, organometallic barium moleties have received renewed attention in recent years, spurred in part, by the search for suitable precursors for employment in the preparation of barium-containing ceramic materials by chemical vapor deposition. In addition to this renewed interest in compositions containing barium-carbon bonds, other classes of reagents which have been examined include barium alkoxides, barium .beta.-diketonates, and barium amides. Other less traditional barium-containing compounds would include Ba(SiPh.sub.3).sub.2, [Ba(P(SiMe.sub.3).sub.2)2(THF).sub.2 ].sub.n and Ba(P(SiMe.sub.3).sub.2).sub.2 .multidot.4 THF. Barium species containing covalent Ba-S interactions have not been studied in detail, perhaps due in part, to the assumption that ligands based on the soft sulfur atom are unsuited for the relatively hard barium ion. Barium is known to form complexes with dithiocarboxylic acids, however these compounds have a highly ionic character. Scant attention therefore, has apparently been paid to barium bis(thiolate) compounds.
The alkaline earth cations, particularly Ba.sup.2+ portray a small charge/size ratio. The large ionic radius of barium demands high coordination numbers (8-12); however, its charge of +2 permits interaction with only two uninegatively-charged ligands, in order to preserve electroneutrality. Many barium compounds of the general formula BaL.sub.2, therefore, reach coordinative saturation by oligomerization and/or catenation, or by solvent molecule incorporation. These compounds, in general, are involatile and insoluble, properties rendering them unsuitable for utilization in chemical vapor deposition. This challenge led to the design of ligands offering the potential for intramolecular stabilization, thereby inhibiting oligomerization.
One example of such a ligand is 2,2-dimethyl-8-methoxyoctane-3,5-dione. The deprotonated ligand forms a stable complex with barium and the resulting compound is a liquid at ambient temperature. A comparable ligand design has been applied to create intramolecularly-stabilized cyclopentadienide complexes of barium. Other examples of ligands offering the potential for intramolecular stabilization are oligoetheralcohols. Barium b/s(oligoetheralkoxide) compounds are liquids at ambient temperature and are monomeric in benzene solution, as determined by cryoscopy. These research efforts have now been extended in the area of intramolecularly-stabilized barium compounds to encompass a new class of compounds, i.e., Group II metal bis(oligoetherthiolates).